The present invention relates to an apparatus and method for the treatment of semiconductor wafers in a treatment tank into which different treatment fluids are successively introduced from respective receptacles or reservoirs to treat the semiconductor wafers.
In the semiconductor industry, it is known to subject semiconductor wafers to a number of chemical wet treatment steps during the manufacture thereof. According to one known system for the chemical wet treatment of semiconductor wafers, the wafers are treated in different process tanks that each contain different treatment chemicals. The chemicals contained in the process tanks are prepared in preparation units and are used for a plurality of substrates or substrate charges. Unfortunately, such systems are relatively large, since a separate treatment tank is provided for each chemical, which leads to high costs for the system. Furthermore, a flexible adaptation of the process sequences is difficult due to the arrangement of the tanks.
Therefore, in recent times so-called single tank systems or Single-Tank-Tools (STT) were developed with a treatment tank into which different treatment fluids were successively introduced from respective reservoirs for the treatment of the wafers. The advantage of such a system is that only a single treatment tank is provided, which considerably reduces the procurement costs for these units. Furthermore, the base or support surface of the units is considerably reduced, which reduces the operating costs, especially if the units are disposed in clean rooms. Known as reservoirs are chemical tanks in which premixed chemicals are stored prior to the introduction into the treatment tank. Alternatively, it is also possible to mix together the necessary treatment chemicals within the respective reservoirs, and to subsequently introduce them into a treatment tank of the unit.
One such single tank system, which is provided with the features of the introductory portion of claim 18, is known, for example, from applicant""s own DE-A-44 13 077. With this single tank system, the treatment chemicals are respectively utilized for one treatment cycle and are subsequently discarded, which leads to a high chemical consumption and thus high cost. Up to now, a reuse of chemicals was not carried out due to the danger of carrying-over of media, which could lead, for example, to crystallization effects.
Proceeding from the above-mentioned state of the art, it is therefore an object of the present invention to reduce the chemical consumption of single tank systems.
Pursuant to the invention, this object is realized in a method for the treatment of semiconductor wafers in a treatment tank into which different treatment fluids are successively introduced from respective reservoirs for the treatment of the semiconductor wafers, and the treatment fluids are conveyed into a collection vessel after a treatment, in that at least a portion of the treatment fluid is conveyed out of the collection vessel back into the respective reservoir, and the collection vessel is rinsed after the conveying-out of the treatment fluid and prior to receiving a further treatment fluid. Since after the treatment, treatment fluid is first conveyed into a collection vessel, the treatment tank can be rapidly emptied in a conventional manner and subsequently, while the treatment in the treatment tank is continued, the treatment fluid can be conveyed out of the collection vessel back into the respective reservoir in order to prepare and reuse it. The rinsing of the collection vessel between the receipt of different treatment fluids ensures that no carrying-over of media can occur between the treatment fluids.
Pursuant to a preferred embodiment, after each treatment in a treatment fluid the semiconductor wafers are rinsed with a rinsing fluid and subsequently the rinsing fluid is conveyed into the collection vessel, whereby it is cleaned in a simple and economical manner.
The treatment fluids are preferably prepared in the respective reservoirs in order to maintain a uniform quality of the treatment fluid. Pursuant to one particularly straightforward embodiment of the invention, the treatment fluids, especially a treatment fluid containing hydrofluoric acid, are topped off to a prescribed volume with treatment fluid from a supply unit in order to achieve a mixture of used and unused treatment fluid. This method is particularly suitable if a greater portion of the treatment fluid is used up during the treatment, or is lost during the transport between treatment tank and reservoir.
Pursuant to a further embodiment of the invention, during the preparation of the treatment fluid, the volume of at least one treatment fluid in the reservoir is determined, the actual concentration of at least one fluid component of the treatment fluid is determined, a required quantity of the fluid component for achieving a desired concentration thereof in the treatment fluid is calculated, and the calculated quantity of the fluid component is introduced into the treatment fluid. The above-mentioned method ensures that the concentration of certain fluid components in a treatment fluid remains the same over a number of treatment cycles. For the determination of the volume, the treatment fluid in the reservoir is preferably topped off with a known fluid component or treatment fluid from a supply unit to a predetermined volume. The measurement of a fluid volume in a reservoir is relatively complex and imprecise. In contrast, the topping-off to a predetermined volume is very simple and furthermore leads to uniform volumes during the calculation of a required quantity of the fluid component. With greatly diluted chemicals, which to a large extent are comprised of water, the treatment fluid is preferably topped off with water as one of the fluid components. Alternatively, treatment fluid can also be introduced from a supply unit in order to reach the predetermined volume.
The concentrations of the fluid components are preferably measured a number of times, and the average value of the measurement is used for the calculation.
The quantities of the required fluid components are preferably calculated with the aid of the following equation:       V    fk    =                                          (                                          K                des                            -                              K                act                                      )                    ⁢                      xe2x80x83                          *            ⁢              xe2x80x83            ⁢                                    V                          bf              ⁢                              xe2x80x83                                              ⁢                      xe2x80x83                          *            ⁢              xe2x80x83            ⁢                                    D            bf                    ⁢                      xe2x80x83                          *            ⁢              xe2x80x83            ⁢                        1000          ⁢                      xe2x80x83                          *                                                  D            fk                    ⁢                      xe2x80x83                          *            ⁢              xe2x80x83            ⁢              K        fk            
where,
Vfk=Volume of the required fluid component in ml
Kdes=Desired concentration of the fluid component (in % by weight)
Kact=Actual concentration of the fluid component (in % by weight)
Vbf=Volume of the treatment fluid in l
Dbf=Density of the treatment fluid in g/ml
Dfk=Density of the fluid component in g/ml
Kfk=Concentration of the fluid component (in % by weight).
For an improved quality, the actual concentration of the fluid component after the introduction of the calculated quantity of the fluid component into the treatment fluid is again measured, and if the actual concentration deviates from the desired concentration, a renewed calculation and introduction is carried out.
Pursuant to one embodiment of the invention, the treatment fluids are displaced out of the processing tank by introducing some other fluid, especially a rinsing fluid, and are conveyed into a collection vessel. This method has the advantage that the semiconductor wafers are continuously covered with a fluid, and are not exposed to the ambient air between different treatment fluids. Furthermore, with this method there results the advantage of a uniform treatment of the semiconductor wafers, since every point of the substrate is retained within the treatment fluid for essentially the same period of time. Due to a partial mixing of the treatment fluid and the other fluid, the entire treatment fluid cannot be recovered, so that media losses occur.
Pursuant to an alternative embodiment of the invention, the treatment fluids are discharged from the processing tank via a rapid discharge valve and are conveyed into a collection vessel. With this method, essentially the entire treatment fluid can be recovered; however, after the discharge of the treatment fluid the semiconductor wafer is initially exposed to the ambient air.
The treatment fluid is preferably circulated in the reservoir in order to achieve a good and uniform mixing of the components of the treatment fluid. In this connection, the treatment fluid is preferably filtered in the reservoir in order to filter out particles that are contained in the treatment fluid and that could adversely affect the treatment of the semiconductor wafers. For a respectively uniform treatment of the semiconductor wafers, the treatment fluid in the reservoir is preferably brought to a prescribed temperature, since the temperature can have a considerable influence upon the success of the treatment. Pursuant to the present invention, at least one treatment fluid contains NH4OH, H2O2, HCl or a combination of at least two of the preceding components, hydrofluoric acid (HF), and/or a sulfur/peroxide mixture (SPM).
The object of the present invention is realized by an apparatus for the treatment of semiconductor wafers, in a treatment tank, with a first valve unit for the introduction of different treatment fluids from different reservoirs into the treatment tank, and at least one collection vessel for collecting the treatment fluid after a treatment, in that a second valve unit is provided for the introduction of at least a portion of the treatment fluid out of the collection vessel into the respective reservoir, and a rinsing unit is provided for the rinsing of the collection vessel. The apparatus has the advantages already mentioned above in conjunction with the method.
The treatment tank preferably has a rapid discharge valve and a collection vessel below the treatment tank or a collection vessel that is embodied as an overflow collar of the treatment tank. If the overflow collar has a relatively small volume, a controllable connection line is preferably provided between the overflow collar and the collection vessel disposed below the treatment tank in order to provide an adequate collection volume for the treatment fluid that is flowing out of the treatment tank. The rinsing unit preferably has at least one fluid nozzle in the collection vessel in order to clean the collection vessel between the receipt of different treatment fluids.